The present invention relates to a detector for use in an infrared gas analyzer for analyzing components in a gas by utilizing absorption of infrared rays, and more particularly to an improved detector employing an infrared-sensing semiconductor element as a light sensor and also a multilayer interference filter.
Heretofore, it has been customary in the conventional infrared gas analyzer to have multilayer interference filters disposed substantially adjacent to a reference cell and a sample cell. The dimensions of the filters are selected to be equal to the area of windows in the cells in order to transmit a sufficient amount of infrared rays. Moreover, since the multilayer interference filter has a temperature coefficient, it is necessary to maintain the filters at a fixed temperature in a high-sensitivity infrared gas analyzer. Consequently the known apparatus is equipped with some suitable means to meet the stable temperature requirement. On the other hand, the infrared-sensing semiconductor element also needs to be kept free from the influence of ambient temperature fluctuation during use, thus it is necessary to provide means to maintain constant the temperature of the infrared-sensing element. Accordingly, the following disadvantages are present in the conventional apparatus: (1) The influence of ambient temperature fluctuation is avoided by providing a temperature control means for each of the multilayer interference filters and the infrared-sensing semiconductor element, or by incorporating the multilayer interference filters and the infrared-sensing semiconductor element in a thermostatic oven. This inevitably renders the infrared gas analyzer structure complicated and expensive.
(2) Since a multilayer interference filter is dimensionally large (substantially equal to the area of a window in the cell), its thermal capacity is great and makes temperature control difficult.
The present invention has been accomplished in an attempt to eliminate the above disadvantages, and an object of the invention is to provide an improved detector for use in an infrared gas analyzer capable of easily achieving temperature control for both the infrared-sensing semiconductor element and the multilayer interference filter.